BUS_ATTACH_CHILDREN(9)

💖 BUS_ATTACH_CHILDREN(9) — manage child devices of a bus device 💖

okay bestie, welcome to the BUS_ATTACH_CHILDREN(9) page from the Kernel Developer's Manual. This is the one about managing child devices of a bus device, and it's lowkey a whole family of functions. Let's get into it. 🫶

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🌸 NAME 🌸

• bus_attach_children, bus_delayed_attach_children, bus_detach_children, bus_enumerate_hinted_children, bus_identify_children — manage child devices of a bus device ✨

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✨ SYNOPSIS ✨

#include <sys/param.h>
#include <sys/bus.h>

void
bus_attach_children(device_t dev);

void
bus_delayed_attach_children(device_t bus);

int
bus_detach_children(device_t dev);

void
bus_enumerate_hinted_children(device_t bus);

void
bus_identify_children(device_t dev);

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💅 DESCRIPTION 💅

okay so picture this: all of these functions are about managing state transitions of the child devices for dev. Slay. Here's the breakdown, bestie:

• bus_enumerate_hinted_children() — walks the kernel environment to identify any device hints that describe a device attached to dev. For each set of matching hints, the BUS_HINTED_CHILD(9) method is invoked. This function is typically called from a bus driver's DEVICE_ATTACH(9) method to add hinted devices. Big note: most bus drivers do not use hints to identify child devices. This is typically used for legacy buses such as ISA that do not provide a mechanism for enumerating devices. 💀
• bus_identify_children() — iterates over all eligible device drivers for children of dev, invoking the DEVICE_IDENTIFY(9) method. This allows device drivers to add child devices that are enumerated via alternate mechanisms such as firmware tables. This function is typically called from a bus driver's DEVICE_ATTACH(9) method. 🌈
• bus_attach_children() — attaches device drivers to all children of dev. This function invokes device_probe_and_attach(9) on each child device, ignoring errors. It makes a best-effort pass to attach device drivers to all children. Child devices are attached in increasing order. Child devices with the same order are attached in FIFO order based on the time when the device was created via device_add_child(9). This function is typically called from a bus driver's DEVICE_ATTACH(9) method after adding devices. 🔥
• bus_delayed_attach_children() — attaches device drivers to all children of dev after interrupts are enabled. This function schedules a call to bus_attach_children() after interrupts are enabled via config_intrhook_establish(9). If interrupts are already enabled (for example, when loading a device driver after booting), bus_attach_children() is called immediately. ⭐
• bus_detach_children() — detaches device drivers from all children of dev by calling device_detach(9) on each child device. Unlike bus_attach_children(), this function does not make a best-effort pass. If a child device fails to detach, bus_detach_children() immediately fails returning the error from the child's failed detach. Child devices are detached in reverse order compared to bus_attach_children(). That is, child devices are detached in decreasing order, and child devices with the same order are detached in LIFO order. Detached devices are not deleted. 🎀

bus_detach_children() is typically called at the start of a bus driver's DEVICE_DETACH(9) method to give child devices a chance to veto the detach request. It is usually paired with a later call to device_delete_children(9) to delete child devices. If no additional logic is required between the two function calls, a bus driver can use bus_generic_detach(9) to detach and delete children. 🦋

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🫶 RETURN VALUES 🫶

The original page leaves this section empty, bestie — no return values are documented here. That's literally it. 💜

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🔥 SEE ALSO 🔥

• config_intrhook_establish(9)
• device_add_child(9)
• DEVICE_ATTACH(9)
• device_delete_children(9)
• DEVICE_DETACH(9)
• device_detach(9)
• DEVICE_IDENTIFY(9)
• device_probe_and_attach(9)

iykyk, these are the friends in the group chat. ✨

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🎀 HISTORY 🎀

• bus_enumerate_hinted_children() first appeared in FreeBSD 6.2. 🌸
• bus_delayed_attach_children() first appeared in FreeBSD 12.2. 🦋
• bus_identify_children() first appeared in FreeBSD 15.0. Its functionality is available in older releases via the deprecated bus_generic_probe(). 💅
• bus_attach_children() first appeared in FreeBSD 15.0. Its functionality is available in older releases via the deprecated bus_generic_attach(). 👑
• bus_detach_children() first appeared in FreeBSD 15.0. Its functionality is available in older releases via bus_generic_detach(). 🌟

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Cute sign-off time: this edition is Debian, dated February 5, 2025, and it's the BUS_ATTACH_CHILDREN(9) manual page. Byeee, bestie 💅✨